A variety of materials have been suggested for use as a core in casting hollow articles or articles having passageways or openings formed therein. One requirement of a suitable core material is that it be readily removable from the casted article. Another requirement is that the core material be non-reactive with the casting materials. Examples of core materials that have been used include glass, salt, carbon, thin walled metal shells, and ceramics.
Recent developments in the metal alloy and casting arts have rendered obsolete the prior art core materials. For example, directionally solidified cast turbine blades made from eutectic composition nickel base superalloys are the leading candidates for withstanding engine operating conditions in advanced gas turbine engines. Since these blades must be air-cooled, they must be fabricated with internal cooling passages. Normally, this is accomplished by casting the molten metal around a ceramic core which is composed of a material inert to the molten metal. Because the directional solidification of eutectic alloys requires the core body to be exposed for longer periods of time to higher temperatures than previously required in casting turbine blades, commercial core materials currently available are unsatisfactory. The lack of a suitable core material is impeding the development of a production process for manufacturing cooled turbine blades from eutectic alloys with aligned microstructures. This in turn limits the temperature capability of the blades, the turbine inlet temperature, and ultimately the improvement in performance of advanced engines.
It is an object of this invention to provide a method for casting hollow articles, utilizing a silicon yttrium or silicon lanthanide oxynitride as the core material.
Another object of the invention is to provide a method for casting superalloys and directionally solidified eutectic alloys in which a self-destructive, non-reactive core material is employed.
Other objects and advantages of the invention will become apparent to those skilled in the art upon consideration of the accompanying disclosure.